Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
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Uncertainty assessment on the configuration of a mechanical
assembly according to tolerance specifications in design
Andrea Magalini, David Vetturi, Luca Pagan
Università degli Studi di Brescia, Dipartimento di Ingegneria Meccanica (Italy)
Alenia S.p.A. - LABEN (Vimodrone, Milano, Italy)
The 1st International Conference on Design Engineering and ScienceOctober 28 - October 31, 2005 Vienna, AUSTRIA
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
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Foreword
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Design to manufacturing deviations from the nominal configuration (restrictions imposed by tolerancing)
Uncertainty related to the final effective three-dimensional configuration of a mechanical assembly
Uncertainty estimation: statistical problem
Metrological analogy (Guide to the Expression of Uncertainty in Measurement - GUM)),...,,( 21 KXXXfY
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
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Planck LFI is an instrument designed to be operative in space.
It is aimed to detect micro waves comingfrom deep space.
With reference to this memory, it is characterised by a number of sensors (feed horns) which must be carefully aligned with a target point.
The following pictures give an overall sight of the instrument and some details of the sensor pack.
The Low Frequency InstrumentIntroduction
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
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BEU
FPU
Waveguides
Su
pp
ort
str
uct
ure
s
1.5
m
The Low Frequency InstrumentOverall Sight
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
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The Low Frequency InstrumentOverall Sight
Horn
LFI HFI
Main Frame
WaveguidesSupportStructure
Waveguides
BEU
Bipodes
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
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The Low Frequency InstrumentFocal Plane Unit FPU
Bipodes Interfacesto satellite
30 GHzfeed horns
70 GHz feed horns
44 GHzfeed horns
HFI
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
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The Low Frequency InstrumentFocal Plane Unit FPU
Feed Horns (1) Main Frame Top (2)
Main Frame (3)
Bipodes (4)
Interfaces to satellite
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
8/22
x
y
z4
3
2
1xL2
yL2
zL2
xL1
yL1
zL1
xL3
yL3
zL3
xL4
yL4
zL4
xA4
yA4
zA4
xA3
yA3
zA3
xA2
yA2
zA2
xA1
yA1
zA1
Local reference frame Coupling reference frame
1 - Feed Horn
2 - Frame top
3 - Main Frame
4 - Exapode
PC
Geometrical ApproachAssembly Modelling
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
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Geometrical ApproachUncertainty Contributions
Dimensional tolerances
Geometrical tolerances
Fit tolerances
Thermal distortions*
Changes of position and orientation of each local reference frame
Fit modalitiesChanges of position and orientation of each local coupling reference frame
*thermal effects are here disregarded
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
10/22
The orientation of each reference frame and the position of its origin can be described in any reference frame by one 4x4 matrix, keeping into account rotations and translations at the same time.
1000z
y
x
ABT
T
T
RM
A B
xB
yB
zB
OB
xA
yA
zA
OA
P
PAV
PBV
OV
1PA
PA
PA
PA z
y
x
V
11z
y
x
BO
BO
BO
O T
T
T
z
y
x
VA
A
A
1PB
PB
PB
PB z
y
x
V
PAPB VMV
Geometrical ApproachHomogeneous Matrixes
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
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ML1 describes the L1 ref. frame in the A1 ref. frame MA1 describes the A1 ref frame in the L2 ref frame ML2 describes the L2 ref. frame in the A2 ref. frame MA2 describes the A2 ref. frame in the L3 ref. frame ...
x
y
z
4
3
2
1xL2
yL2
zL2
xL1
yL1
zL1
xL3
yL3
zL3
xL4
yL4
zL4
xA4
yA4
zA4
xA3
yA3
zA3
xA2
yA2
zA2
xA1
yA1
zA1PCML1
MA1ML2
MA2ML3
MA3ML4
MA4
1PCV
PCV Position vector of the
PC in the L1 ref. frame
Geometrical ApproachHomogeneous Matrixes
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
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x
y
z
4
3
2
1xL2
yL2
zL2
xL1
yL1
zL1
xL3
yL3
zL3
xL4
yL4
zL4
xA4
yA4
zA4
xA3
yA3
zA3
xA2
yA2
zA2
xA1
yA1
zA1PCML1
MA1ML2
MA2ML3
MA3ML4
MA4
1PCV
1PCV Position vector of the
PC in the L1 ref. frame
PCV Position vector of the PC
in the absolute ref. frame
11
1
1
1z
y
x
PC V
V
V
V
1144332211 PCPCALALALALPC VMVMMMMMMMMV
1z
y
x
PC V
V
V
V
Position of the PC (x,y,z)FH orientation(angles given following any chosen rule)
M
Geometrical ApproachHomogeneous Matrixes
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
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Local frame L1: origin in correspondence of the P point x axis correspondent to the FH real axis y axis passing from the centers of the pins
locations
Coupling frame A1:
origin in the theoretical P point (on the FH)
x axis correspondent to the FH theoretical axis
y axis passing from the centers of the pins locations
FH 44 GHz
x
y
z
P P z
y
xx
Tolerancing Specifications EffectsReference frames definition
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Drawings are courtesy of Alenia S.p.A. - LABEN
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
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1. translation along x of the L1 origin
2. rotations around A1 z & y axis
3. pins location in the yz plane: translations in y and z of the L1 origin and rotation around the A1 x axis (general dimensional tolerance)
Tolerancing Specifications EffectsUncertainty Contributions
1 3
2
x
y
z
P
x
y
z
P
P z
y
xx
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Drawings are courtesy of Alenia S.p.A. - LABEN
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
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The shown uncertainty causes produce a modification of the orientation of the L1 ref. frame as regards the A1 ref. frame (2 & 3) and a translation of the L1 origin in the A1 ref. frame (1).
There are further uncertainty contributions relating the uncertainty connected to the theoretical position of the PC: they influence the components of the position vector for the PC in the L1 ref. frame.
Tolerancing Specifications EffectsUncertainty Contributions
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
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Numerical Statistical Analysis
),...,,( 21 nXXXfY
MCS INPUT Model :
Probability density functions g(Xi) for each Xi
Number M of Monte Carlo trails
Coverage probability P%
MCS CALCULATION
M samples xi1, xi2, …, xiM of Xi are generated according to g(Xi)
M values for Y are calculated according to the model f:
PRIMARY MCS OUTPUT
Sample of possible values for Y: approximation of the Y pdf g(Y)
MCS RESULTS Estimate of y value for Y and associated standard uncertainty u(y)
Coverage interval for Y: [ylow, yhigh]
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...
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21
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121111
NMMMM
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N
xxxfy
xxxfy
xxxfy
)(XfY
Mon
te C
arl
o M
eth
od
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
17/22
Using the Monte-Carlo simulation technique, for each uncertainty contribution, a series of M values is generated within the range of values defined by the considered tolerance (suitable distribution function).
A series of M vectors, representing the M different situations is found, in consequence of the considered tolerances.
For each situation (vector), the rotation-translations matrixes are computed.
Numerical Statistical AnalysisMonte Carlo Simulation
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
18/22
Three angles, defining the orientation of the feed horn, are extracted from the total M rotation-translations matrix.
The position of PC in the absolute ref. frame is obtained by the product of the M matrix and the VPC1 vector.
The three found rotations and the the three found translations give the FH space location.
Numerical Statistical AnalysisMonte Carlo Simulation
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
19/22
The six degrees of freedom (position of the PC, orientation of the FH axis) of the FH are considered as random variables.
For each random variable a series of M possible numerical values has been obtained by the previously explained method.
Starting from the M values (constituting a sample), available for each variable, a proper probability distribution can be computed for this (its parameters are estimated). So a mean value and a standard deviation are calculated for the six degrees of freedom.
Numerical Statistical AnalysisMonte Carlo Simulation
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
20/22
Qualitative ResultsA FH d.o.f.
Phase Center position - z axis
f(x)
Simulation
Histogram
Theoretical
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Qualitative results
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
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General statistical method based on the Monte Carlo simulation technique for the uncertainty estimation
Can be adopted for: uncertainty estimations, sensitivity analysis, quality evaluation of design
Generality: non-linear problems, multi-output problems, whatever kind of probability distribution function
Improvements: adaptive Monte Carlo, closed-loop geometry structures
Conclusions and DiscussionMethod
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan
Università degli Studi di BresciaDipartimento di Ingegneria Meccanica
22/22
... thank you Authors are grateful to:• ALENIA S.p.A. - LABEN (Vimodrone, Italy) • CENTROTECNICA S.a.S. (Milano, Italy)
Uncertainty assessment on the configuration of a mechanical assembly according to tolerance specifications in designA. Magalini, D. Vetturi, L. Pagan